The present invention relates to an energy absorbent medium and, in particular, to a polymeric based material for absorption and dispersion of impact energy which is formable into articles useful in the protection of animate and inanimate objects.
Padding materials and structures have been developed to protect animate objects such as the human body, and inanimate objects which are susceptible to injury or damage when subjected to shock, vibration or stress.
In a number of contexts the human body requires protection from external impact and vibration beyond the normal protection afforded by the structure of the body itself. For instance, impact stress is a significant concern in contact sports such as football, hockey and soccer in which the participant is periodically or constantly subject to high impact stress. Bruising, fracture, joint impact trauma and osteoarthritis, susceptibility to sprains, muscle cramps, tendinitis, and strains, fatigue, and discomfort are all incidents of such impact stress being imparted to the body of the participant.
Another example of high impact stress attenuation is represented by the absorbent of seats, steering wheels, and structures surrounding the driver of a vehicle, designed to cushion the body of the driver in motor sports.
For those who are confined to bed, in wheel chairs, or in body contact with other medical implements requiring prolonged contact between the body and the implement, the difficulties can be quite substantial. As those involved in the field well understand, substantial problems arise from contact between the body and articles which require prolonged contact with the body, such as medical devices, prosthetics, orthopedic implements, such as casts, braces and the like, aids for the disabled such as wheelchairs, crutches, beds for those who are confined there. Through prolonged or high stress contact, a variety of undesirable consequences often plague the users of such constructs. Problems range from ulcerations (bed sores), to dermal inflammation, blisters, and simple irritation and discomfort.
Padding in use today for energy dissipation, cushioning or shock absorbing applications is typically made of assorted foams, urethanes and plastic, rubber, and metal. The materials are formed into shape by stitching, die cutting, molding or shearing. Pre-formed pads are made in various sizes that conform over a limited range of applications. Pads molded from foams produce a solid, semi-stiff piece. Although molded pads may be custom fit to an object or an individual, they are not compliant to the object or user. Molded pads, for instance, do not change shape as the anatomy of the user may change during a given activity. For example, a jet fighter pilot""s body changes under g-forces and may swell at higher altitudes. Another example is present in motorsports where a race car driver can lose over ten pounds during a race, in which case a custom molded seat would then be too loose and not provide the needed support. Metal pads offer protection against shock, however lack comfort and are not lightweight and provide little or no vibration protection. In some instances metal pads are the cause of damage.
Polymer gel padding is currently being used in applications where cushioning is required. The gels are typically manufactured from silicone and urethane elastomers which are cross linked into specific geometries. The gel pads are extremely soft and easily compressed, but do not flow and could not be classified as a fluid. When weight is applied the gel pad is soft enough that it will collapse to support the weight, but only in a single dimension. It is generally recognized that polymer gel padding does not offer significant shock protection or protection from side-to-side motions or g-force loading. The person or object will typically move around in the padding since it will not shear. In many instances the object to be protected may xe2x80x9cbottom outxe2x80x9d within the padding. These padding materials are typically of higher specific gravity than the current invention which incorporates lower specific gravity fillers.
It would be particularly beneficial to produce a padding composition which overcomes the limitations of current padding, and which also exhibits the capability to change the padding""s physical characteristics in response to applied loads or forces.
Traditional padding does not generally maintain intimate contact with the portion of a human body to be protected. In order for the body to be totally supported by the padding, the substrate material must crush to accommodate the contours of the body. Under sudden applied force, a human body or inanimate object will often move around within the voids between the padding and the user or object.
Accordingly it is a principal object of the present invention to provide compositions, structures and padding articles made therefrom which are conformable to the surface of an animate or inanimate object, and which responds to an applied force or stress by minimizing the transfer of such force or stress to the object.
It is an object of the present invention to provide for prolonged or high impact or vibration stress contact structures which respond elastically to applied impact forces between an animate or inanimate object and the structure to limit peak impact force applied to the object.
It is an object of the present invention to provide padding articles for use in contact sports such as football, hockey, soccer and basketball that are conformable to the human body and which exhibit the characteristic of a viscous liquid in the absence of a sudden applied force, and convert to a near solid elastomer in response to a high rate applied force to minimize the transfer of the force to the human body.
It is an object of the present invention to provide padding articles which respond elastically to applied vibration and forces between an object and the article to attentuate the vibration and force applied to the object.
It is another object of the present invention to provide articles for prolonged or high impact or vibration stress contact which are highly conformable to, and supportive of, the object surface configuration.
It is a further object of the present invention to provide for prolonged or high impact or vibration stress contact structures which respond resiliently to applied impact forces between an object and the structure with controlled or tuned elastic hysteresis.
An additional object of the present invention is to provide for prolonged or high impact or vibration stress contact absorbent, cushions, and like structures which provide for improved tolerance of the human body to contact with medical appliances and related structures and articles, including neck braces, wheel chair cushions, bed pads, absorbent for orthopedic appliances such as braces, casts and the like.
Generally, the present invention provides a high impact energy absorbent medium comprising the use of a conformable, resilient component which includes an envelope containing a polyborosiloxane elastomer. The response of the system to applied force optimizes high impact and vibration and repetitive impact shock absorption. The high level of conformability is a key to preventing adverse consequences of prolonged contact.
The invention is a self-conforming, compliant, high impact energy absorbent medium that continuously conforms to the environment in which it is used. At rest the medium acts as a viscous liquid and it offers conformal cushioning and support for a protected object. When a sudden or high rate impact force is applied to the medium it becomes dilatant and rheopectic which causes the composition (a thermo-rheologically complex fluid) contained within an envelope defining a padding article, to become more rigid (or viscous) with an increasing rate of deformation. The medium will stiffen and dissipate energy in accordance with the rate of the force applied to the article. When the external force is not present or is of low rate impact, the medium returns to a lower elastic modulus state and its original conforming condition. The term xe2x80x9crheopecticxe2x80x9d defines the property of a composition in which elastic modulus increases with time under shear or suddenly applied force or stress.
In the broadest terms, the present invention provides an energy absorbent and form compliant article for cushioning animate and inanimate objects comprising a pliable, conformable confinement means for containing and controlling the shape and placement of an energy absorbent medium, and a highly conformable and energy absorbent medium confined within said confinement means comprising a visco-elastic, plasticized rheologically dilatent, polymer composition. The polymer exhibits reformable sacrificial chemical bonds which are preferentially broken under high shear conditions and yet quickly reform under low stress conditions.
As used herein viscoelasticity refers to the property of having a high viscosity fluid characteristic under low stress conditions and exhibiting a substantial increase in apparent viscosity under applied stress, so that the material behaves as a solid under such high applied stress conditions. In the context of the present invention, a viscoelastic material is one which behaves as a solid elastomer under high rate impact forces, and as a highly conformable viscous liquid under rest or when subject to a low rate of applied force.
By providing a controlled hysteresis, the absorption of energy by elastic compression can be carefully tuned to serve the requirements of use in a highly protective and efficient fashion. In like fashion, it is possible to control, within limits, the proportion of applied energy returned and transmitted by any elastic rebound, and the proportion dissipated or absorbed and changed into other forms of energy, i.e. heat.
In static circumstances or under a low rate of applied or impact force, the material conforms to the object with which it is in contact by viscous flow. The viscous flow is limited and constrained by the containment system so that it does not result in the material flowing out of areas to be protected. While the composition of the present invention is responsive to stresses by viscous flow, the effect is largely an elastic deformation and flow is limited in the usual time span of normal stresses. At moderate to high stress, such as the imposition of sudden impact, and consequently a high rate of applied force, the material deforms and absorbs or dissipates the imposed energy by viscoelastic deformation or elastic compression. Both the rate of energy absorption, resulting from deceleration of the impact force, and the rate of elastic rebound are controlled by determining the elastic hysteresis. The major effect is spreading the energy transfer associated with the sudden impact over a much greater time span so that the peak incident force levels transferred to the object are reduced.
Upon exposure to prolonged or sudden impact or other stresses, and particularly applied stresses beyond the viscoelastic limit, the polymer cross-link bonds are broken, absorbing energy of the impact, and xe2x80x9cdeadeningxe2x80x9d the impact. Polymer chain scission is minimized by the preferential breaking of the cross-link bonds. The energy which breaks the chemical bonds is converted largely to heat. The broken cross-link bonds will be reformed, and the polymer thus has a very substantial life span. Very effective protection from polymer degradation can be provided for a prolonged life of articles in such fashion.
The articles of the present invention preferably employ a borosiloxane elastomer which may be formulated to provided an optimal response to the applied dynamic loading. The high energy absorbent comprises a containing envelope and a polyborosiloxane elastomer composition contained therein. The absorbent envelope can be formed in a variety of shapes and thicknesses. The time required to recover and the actual restoring forces are typically based on the thickness of the structure, as defined by the confining envelope and associated structures; the apparent viscosity, rebound, plastic flow and related properties of the polymer under the applied stress; and the inherent time-dependent response, i.e. hysteresis, of the polymer formulation. Varying any of these properties will also vary the recovery rate of the absorbent article.
The containment envelope may be formed using any flexible material such as a film or sheet of a flexible plastic material, or relatively non-porous fabric, foil, leather, or the like so long as its mechanical and chemical integrity are sufficient to contain a silicone polymer with fluid like behavior.
Polyborosiloxanes have unique elastomeric properties. The fluid will dramatically increase its apparent viscosity to behave as a near solid under sudden impact or shear, a property known in the art as viscoelasticity. This property increases lateral support and impact damping. Under low rates of applied force or stress, polyborosiloxanes readily flow, but under a high rate of applied force or stress they exhibit an increase in apparent viscosity, high compression modulus, and high elastic rebound. These materials also are extremely resilient and experience little permanent deformation after repeated loading. This makes polyborosiloxanes unique as an energy absorbent medium. In addition, the hysteresis of polyborosiloxanes can be altered to optimize the properties for specific applications and environments by the addition of lubricants (plasticizers or dilutents), fillers (thickeners), and the like.
In operation, when the energy absorbent medium described above is installed in an article, such as a sports pad or glove, designed for body contact, it operates to provide the wearer with protective shock absorption and energy dissipation. A significant beneficial characteristic of such a padding article is the ability to adjust or tune the hysteresis and plastic flow when stress is applied to the polymer.
The rebound rate of the article may be tuned to meet the needs of a particular user and/or a particular activity. These factors in combination determine the dynamic loading to which the recovery rate of the article may be tuned. Through tuning, the maximum shock absorption capabilities may be achieved for a variety of specific applications.
Polyborosiloxane elastomers have a wide range of properties and can easily be tailored to a specific viscosity, time dependent mechanical response (elastic hyteresis) and other desirable properties. Borosiloxane polymers can be polymerized or formulated to have a range of relaxation times spanning several orders of magnitude at room temperature.
A high degree of adjustment may be achieved through blending different polyborosiloxanes and by compounding the polymer with lubricants and fillers. The containment envelope itself may be varied in shape, dimensions and details of configuration depending upon the characteristics of the particular application.
For the compounding of the polymer and tuning the hysteresis and related properties, lubricants such as silicone oils, fatty acids, and fatty acid salts and greases may be used. Solid particulate fillers such as solid particulate or fibrous fillers, such as silica, or microspheres of silica, phenolic resins or thermoplastics, may be used.
The above-described novel high impact energy absorbent material compositions have numerous uses and applications. The following are representative padding article applications illustrative of the breadth of beneficial uses for the novel absorbent material compositions:
(1) Sports padding articles such as shoulder pad lining, rib protection, shin guards, hip and thigh pads in athletic gear. The protective high impact energy absorbent composition may also be embodied in the form of a bandage, elastic sleeve, or the use of wrapping material such as gauze to secure the composition to protect the limb of a human body in addition to the use of a padding article;
(2) Hand protecting padding articles, including gloves, for use in sports and industry;
(3) Seat padding articles for motor vehicles such as race car absorbent in seats to dissipate high vibration, g-force side-loads and shock. The high impact energy absorbent response of the seat padding article will relieve pressure points created by uneven, rough road surfaces hard seating surfaces and crashes;
(4) Medical padding articles for use as xe2x80x9cblocksxe2x80x9d to support patients during procedures such as X-ray, neck braces, or as conformal absorbent and cushioning to uniformly support the body weight of persons with limited or no motor skills such as a paraplegic. Such padding articles can be used to support body weight without allowing pressure points, without allowing the material to xe2x80x9cbottom outxe2x80x9d or without allowing the material to take a xe2x80x9cone-time setxe2x80x9d to a particular shape as is the case with many traditional padding materials. The absorbent medium can be used to support a person in a sitting position (i.e., a wheelchair) or laying flat (i.e., a hospital bed). The medium will totally conform to the user without creating voids between uneven surfaces and the anatomy of the patient;
(5) Extreme trauma protection padding articles for use in combination with other protective gear. A bullet proof vest with the novel medium as a backing will produce a vest that dissipates the energy transferred through the vest after being impacted by a bullet;
(6) Subsurface padding articles for use, as an example, beneath an artificial surface of an athletic field to provide cushioning and energy dissipation to provide comfort and reduce injuries. The padding article for an athletic field may consist of a number of separate xe2x80x9ccellsxe2x80x9d exhibiting different impact response characteristics. For example, the infield area of a baseball field could be made xe2x80x9csofterxe2x80x9d than the outfield area.
(7) Industrial and military equipment padding articles to provide shock and vibration dissipation in applications such as motor mounts, and mounts for weaponry on board naval ships;
(8) Packaging padding articles to protect objects such as electronic equipment during shipping; and
(9) In situ padding articles that can be formed in the field to protect an injured area of a person from further injury by placing the conformal absorbent medium in contact with the injured area and placing a conventional wrap over the medium to secure it.
It has been found that the requirements of protecting an object, including the human body from impact, vibration, repetitive stress and prolonged contact stress can be enhanced by articles or structures containing the novel composition which afford several specific characteristics.
The structures to be employed should provide the maximum contact surface consistent with the required configuration of the structure or the article or device of which it is a part;
The structures must be highly conformable to the body surface configuration;
The structures must freely change conformation to preserve high conformity to the body surface configuration with changes in position or posture of the body;
The structure should respond elastically to a high rate of applied impact forces between the body or object and the structure; and
The structure ordinarily should not impair or interfere with normal body functions such as limiting the range of motion or the like.
It has been found that the requirements of protecting the body from high kinetic energy impact stress can be enhanced by structures which afford several additional specific characteristics;
Attenuation is, in part, a function of both elastic and plastic or fluid deformation. Impact energy should be transmitted through the medium in lateral directions, at angles to the axis of the impact motion, i.e., spreading the impact energy over as wide an area as possible;
Attenuation is also, in part, a function of the time for transmission of stress to the body. An impact force varies with the square of the speed;
An important additional factor is the rate and magnitude of elastic rebound.
The requirements of these two major categories of object contact and protection share a substantial number of common considerations and demands and are generally similar, except that the high impact protection has additional criteria not required of low stress, prolonged contact.
The demands of repetitive motion stress and vibration protection share the requirements of both prolonged body contact and high impact stress, and have additional requirements and characteristics.
The present invention provides a cushioning and energy-absorbent medium and articles made therefrom which meet these criteria, for both static and low-stress prolonged contact and for high rate impact contact in a highly effective manner to provide for superior performance when compared to the padding and cushioning materials of the prior art.